If they did so without paying taxes they'd be violating the tax laws. Why would they risk it, since the profits to be had would no longer be inflated by anti-pot laws? People who make money babysitting, mowing lawns, housecleaning, etc. technically should be paying taxes too, but how many do you suppose actually are?
The off-the-books dealer making no more than a babysitter ... him I'm not worried about.